1. Field of the Invention
The present invention relates generally to data recovery systems and more particularly to multiple frequency data recovery systems for use in disk drives.
2. Description of the Prior Art
Data storage devices such as tape and disk drives are well known in the art. These systems use various clocking and data recovery systems. Examples include U.S. Pat. No. 4,617,599, issued to T. Noguchi, et al; U.S. Pat. No. 4,433,424, issued to L. Taber, et al; and U.S. Pat. No. 4,357,707, issued to D. Delury.
Some data storage devices require the reading of various densities or bit rates when recovering data from the media used. This requirement occurs in disk drives as well as tape drives. For example, a standard 51/4 inch floppy disk drive (FDD) uses forty-eight tracks per inch and has a data rate of five hundred kilobits per second. A more efficient version of the FDD has ninety-six tracks per inch with a transfer rate of eight hundred kilobits per second. Recently, Konica Technology, Inc. has introduced a 51/4 inch FDD which achieves four hundred and eighty tracks per inch and a transfer rate of sixteen hundred kilobits per second. This new FDD is also compatable with the older forty-eight and ninety-six tracks per inch disks.
In order to accomplish the recovery of data on disks having three different densities, it is necessary to have three selectable phase locked oscillators (PLO) plus three selectable delays for optimization of the data recovery system. Present day drives do not generally use discrete PLOs. Instead the data recovery system, including the PLO, are constructed on a single integrated circuit (IC).
One way to accomodate data recovery in a three density system is to use three different data recovery ICs. However, this results in increased cost and space. What is needed is a way to adapt a single data recovery IC for use at multiple frequencies.